fix: fix _get_files_in_folder recursive error

[fatelei]

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Summary

fix #36281

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	0.00%	44.40%	+44.40%
Strict coverage	0.00%	43.93%	+43.93%
Typed symbols	0	22,518	+22,518
Untyped symbols	0	28,501	+28,501
Modules	0	2558	+2,558